<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <link rel="stylesheet" href="./style/my.css" />
    <!-- 引入 Bootstrap -->
    <!-- <link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet"> -->
    <style>
        #myid{
            background-color: orange;
        }
        div{
            background-color: green;
        }
        .myclass{
            background-color: blue;
        }
        span.ak{
            /* 0011 */
            background-color: green;
        }
        .ak{
            /* 0010 */
            background-color: red !important; 
        }
        
    </style>
</head>
<body>
    <div class="myclass" id="myid">
        123
    </div>

    <span class="ak">按钮</span>
</body>
</html>